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transistor

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Please post a schematic or drawing of what you want to do and I might be able to help.
 
im hoping the transistor is pnp,
this is a motor speed controller i have left out some protection devices like diodes.
this uses a 24v batetry and can deliver 200Ah! the motor is 40 amp
 

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danielsmusic said:
im hoping the transistor is pnp,
this is a motor speed controller i have left out some protection devices like diodes.
this uses a 24v batetry and can deliver 200Ah! the motor is 40 amp
If those resistor values are correct, the transistors would have to be Darlingtons if they were gonna deliver tens of amps.
What do you mean by "200Ah"? That's a battery capacity rating.
 
what in the world type application would require a DC motor to pull 40 amps from a 24v power supply? It sounds like locked rotor amps. This motor coil sounds practically like a dead short! I'm not saying I don't believe it, it just seems rather odd. Is this in some kind of electric car or something with a lot of torque?
 
This also isn't a practical speed controller scheme, dissipation in the transistors would be EXTREMELY high, they would fail S/C, probably within a few seconds?. Try doing the maths "Watts = Volts x Amps".

I suggest you try looking up PWM speed control, which is the only practical method of doing it - be aware, it's NOT simple, and it's NOT cheap, but it does work well if designed correctly.

For some helpful info try https://www.4qdtec.com/#mot.
 
well the motor is old and 1/2 horse power. 200Ah is a battery rating.
sorry, what is a S/C
 
danielsmusic said:
well the motor is old and 1/2 horse power. 200Ah is a battery rating.
sorry, what is a S/C

A "Short Circuit", likewise O/C is "Open Circuit".

But your crude voltage regulator is no way to control a motor, certainly not anything big enough for 200Ah lead acid batteries :lol:
 
The pot in the circuit will adjust the motor's speed just fine if the motor doesn't have a load. Add a load to the motor and it won't have enough torque to start turning and the transistors used as a linear resistor will burn.
 
Hi Danielsmusic,
The paralleled transistors in your circuit act like a resistor in series with the motor. When the motor is loaded, its current requirement will increase. But the "resistor" in series with it will have more voltage drop across it when the motor tries to draw more current, resulting in less voltage (and current) for the motor and therefore a loss of torque.

Pulse-Width-Modulation is used in wheelchairs and golfcarts and applies full power to the motor in pulses at a very high rate. The duty-cycle of the duration of the pulses compared with the duration of the off-time determines the speed of the motor. A tachometer can also be used to vary the width of the pulses so that the speed of the motor remains constant with a changing load, or when starting.
Since the transistors fully switch on and off, they don't heat nearly as much as transistors used as a resistor. :lol:
Win-win. Lotsa torque and not much heating.
 
thanks iv seen this before, do i connect the negetive of the motor the the collector of the transistor.
normally i would connect the positive of the motor to the emiter not the battery.

iv done somthing like this before, a relay operated from a computers parralel port
 
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